1. Technical Field
The present application relates to an image forming apparatus, image forming method and image sensor.
2. Description of the Related Art
A two-dimensional image sensor in which a lot of photoelectric conversion sections are arranged in columns and rows within its imaging surface has been used as an image sensor for an image capture device. Each of those photoelectric conversion sections is typically a photodiode which has been formed on a semiconductor layer or on a semiconductor substrate, and generates electric charges based on the light incident thereon. The resolution of the two-dimensional image sensor depends on the arrangement pitch or density of the photoelectric conversion sections on the imaging surface. However, since the arrangement pitch of the photoelectric conversion sections has become almost as short as the wavelength of visible radiation, it is very difficult to further increase the resolution.
An image captured by the image sensor is comprised of a lot of pixels, each of which is defined by a unit region including a single photoelectric conversion section. Since there is an area to be occupied by wiring on the imaging surface, the photosensitive area R2 of a single photoelectric conversion section is smaller than the area R1 of a single pixel. The ratio (R2/R1) of the photosensitive area R2 to the area R1 of each pixel is called an “aperture ratio”, which may be approximately 25%, for example. If the aperture ratio is low, the amount of light that can be used for photoelectric conversion decreases, and therefore, the quality of a pixel signal to be output by the image sensor declines. However, by adopting a configuration in which an array of micro lenses is arranged to face the imaging surface and in which each of those micro lenses faces, and converges light onto, its associated photoelectric conversion section, the photosensitive area R2 can be increased so effectively that the aperture ratio (R2/R1) can be raised to the vicinity of one. Nevertheless, even if the aperture ratio (R2/R1) is increased in this manner, the arrangement pitch and arrangement density of pixels do not increase, and therefore, the resolution does not change.
Japanese Laid-Open Patent Publication No. 2006-140885 discloses how to increase the resolution by super-resolution technique. To increase the resolution by such a technique, restoration needs to be done by deconvolution, and therefore, a point spread function (PSF) should be obtained. For example, to determine the PSF actually, a dotted light source needs to be used. That is why it has been proposed that the PSF be obtained using quantum dots or fluorescence beads.
However, it is difficult to obtain the PSF accurately. In addition, since the magnitude of the PSF is proportional to the zoom power of shooting, the measuring error of the PSF increases proportionally to the zoom power of shooting. As a result, the quality of the high-resolution image deteriorates proportionally to the resolution.